The invention relates to polmyerizable mesogenic tolanes, to polymerizable liquid crystal compositions comprising the polymerizable mesogenic tolanes, to linear or crosslinked liquid crystal polymers obtainable from the polymerizable mesogenic tolanes and the compositions comprising them, and to the use of the polymerizable mesogenic tolanes, and the polymerizable compositions and polymers obtained thereof in optical elements, liquid crystal displays, adhesives, synthetic resins with anisotropic mechanical properties, cosmetics, diagnostics, liquid crystal pigments, decorative and security applications, nonlinear optics and optical information storage.
Polymerizable mesogenic compounds, which are also known as reactive mesogenic compounds, have been described in prior art for various purposes. For example, they can be aligned in their liquid crystal phase and subsequently polymerized in situ, to give linear or crosslinked liquid crystal polymer films with uniform orientation of high quality. These films can be used for example as optical elements, like polarization filters as described in EP 0 397 263, broadband circular polarizers as described in EP 0 606 940 and WO 97/35219, or compensation or retardation films as described in WO 98/00475, WO 98/04651 or WO 98/12584.
The polymerizable mesogenic compounds described in prior art, however, do often exhibit liquid crystalline phases only in a small temperature range or do not show mesophase behavior at all. Furthermore, polymerizable mesogenic compounds of prior art do often exhibit only low or moderate values of the birefringence.
When preparing oriented liquid crystal polymer films for the uses as described above, it is especially desired to have available polymerizable compositions exhibiting a nematic liquid crystal phase at room temperature, so that it is possible to carry out alignment and polymerization of the composition at low temperatures. For this purpose, it is advantageous if the single polymerizable components exhibit broad liquid crystalline phases, too.
Thus, there is a demand for polymerizable mesogenic compounds with a broad liquid crystalline phase and a high birefringence, which can be used for the preparation of oriented liquid crystal polymer films for optical applications.
Furthermore, regarding the broad range of applications for polymerizable mesogenic compounds it is desirable for the expert to have available further compounds of this type which are easy to synthesize and fulfill the various requirements as described above.
It was an aim of the invention to provide polymerizable mesogenic compounds with advantageous properties, thus extending the pool of reactive mesogenic compounds available to the expert. Other aims of the present invention are immediately evident to the person skilled in the art from the following detailed description.
Upon further study of the specification and appended claims, further objects and advantages of this invention will become apparent to those skilled in the art.
It was now found that these aims can be achieved by providing polymerizable mesogenic tolanes according to the present invention.
Polymerizable mesogenic compounds comprising a tolane group are disclosed in WO 98/52905, EP 0 659 865, JP 11-147853, JP 11-080090, JP 08-231958, JP 07-109351 and JP 07-017910.
The terms reactive or polymerizable mesogenic compound as used in the foregoing and the following comprise compounds with a rod-shaped, board-shaped or disk-shaped mesogenic group, i.e. a group with the ability to induce mesophase behavior. These compounds do not necessarily have to exhibit mesophase behavior by themselves. It is also possible that these compounds show mesophase behavior only in mixtures with other compounds or when the polymerizable mesogenic compounds or the mixtures comprising them are polymerized.
One object of the present invention are polymerizable mesogenic tolanes of formula I 
wherein
P is CH2xe2x95x90CWxe2x80x94COOxe2x80x94, WCHxe2x95x90CHxe2x80x94Oxe2x80x94, 
xe2x80x83or CH2xe2x95x90CHxe2x80x94 Phenyl-(O)kxe2x80x94 with W being H, CH3 or Cl and k being 0 or 1,
Sp is a spacer group having 1 to 25 C atoms,
X is xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94COxe2x80x94NHxe2x80x94, xe2x80x94NHxe2x80x94COxe2x80x94, xe2x80x94CH2CH2xe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94CH2Oxe2x80x94, xe2x80x94SCH2xe2x80x94, xe2x80x94CH2Sxe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94Cxe2x89xa1Cxe2x80x94, or a single bond,
n is 0 or 1,
Z1 and Z2 are each independently xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94CH2CH2xe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94CH2Oxe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94Cxe2x89xa1Cxe2x80x94, or a single bond,
A1 and A2 are each independently 1,4-phenylene in which, in addition, one or more CH groups may be replaced by N, 1,4-cyclohexylene in which, in addition, one or two non-adjacent CH2 groups may be replaced in each case by O or S, 1,4-cyclohexenylene, 1,4-bicyclo(2,2,2)octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl, or 1,2,3,4-tetrahydro-naphthalene-2,6-diyl, it being possible for all these groups to be unsubstituted, mono- or polysubstituted with F,Cl, OH, CN, NO2 or alkyl, alkoxy or alkanoyl groups having 1 to 7 C atoms wherein one or more H atoms may be replaced by F or Cl,
m1 and m2 are each independently 0, 1 or 2, with m1+m2 less than 3,
L1 and L2 are each independently F, Cl, CN, OH, NO2 or an alkyl, alkoxy or alkanoyl group having 1 to 7 C atoms wherein one or more H atoms may be substituted by F or Cl,
r is in each case independently 0, 1, 2, 3 or 4,
R is H, CN, halogen or a straight-chain or branched alkyl radical with up to 25 C atoms which may be unsubstituted, mono- or polysubstituted by halogen or CN, it being also possible for one or more non-adjacent CH2 groups to be replaced, in each case independently from one another, by xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94NHxe2x80x94, xe2x80x94N(CH3)xe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94OCOxe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94COxe2x80x94, xe2x80x94COxe2x80x94Sxe2x80x94 or xe2x80x94Cxe2x89xa1Cxe2x80x94 in such a manner that oxygen atoms are not linked directly to one another, or alternatively R is Pxe2x80x94(Spxe2x80x94X)nxe2x80x94.
with the provisos that
a) in case P is CH2xe2x95x90CWxe2x80x94COOxe2x80x94 or 
xe2x80x83and m1+m2 is 0, then R is Pxe2x80x94(Spxe2x80x94X)nxe2x80x94 and/or at least one r is different from 0,
b) in case P is CH2xe2x95x90CWxe2x80x94COOxe2x80x94 and one of xe2x80x94(A1xe2x80x94Z1)m1xe2x80x94 and xe2x80x94(A2xe2x80x94Z2)m2xe2x80x94 is substituted or unsubstituted phenylene and the other is a single bond, then R is Pxe2x80x94(Spxe2x80x94X)n and/or n is 1,
c) in case m1+m2 is 2, then A1 and A2 are not cyclohexylene.
Another object of the invention is a polymerizable liquid crystal composition comprising at least two polymerizable components, at least one of which is a compound of formula I.
Another object of the invention is a linear or crosslinked polymer obtainable by polymerization of one or more compounds of formula I or of a polymerizable composition comprising one or more compounds of formula I.
Yet another object of the invention is the use of a compound of formula I, or a polymerizable composition or polymer obtainable thereof, in optical elements such as polarizers, optical retardation or compensation films, alignment layers, colour filters or holographic elements, in liquid crystal displays such as PDLC (polymer dispersed liquid crystals), polymer gel or polymer stabilized cholesteric texture (PSCT) displays, in adhesives, synthetic resins with anisotropic mechanical properties, cosmetics, diagnostics or liquid crystal pigments, for decorative and security applications, and for nonlinear optics or optical information storage.
Especially preferred are compounds of formula I wherein
m1+m2xe2x89xa71
at least one of A1 and A2 is an aryl group as previously described, preferably when m1+m2=1,
one of m1 and m2 is 1 and the other is 0,
m1 is 1 and m2 is 0,
at least one of Z1 and Z2 is xe2x80x94COOxe2x80x94 or xe2x80x94OCOxe2x80x94,
R has one of the meanings given for Pxe2x80x94(Spxe2x80x94X)nxe2x80x94,
R is halogen, cyano or an optionally fluorinated achiral or chiral alkyl or alkoxy group with 1 to 15 C atoms,
n is 1,
Sp is alkylene with 1 to 12 C atoms,
X is xe2x80x94Oxe2x80x94 or a single bond.
Of the compounds of formula I wherein P is CH2xe2x95x90CWxe2x80x94COOxe2x80x94 especially preferred are those wherein n is 1.
Of the compounds of formula I wherein m1+m2 is 1 or 2, especially preferred are those wherein n is 1, those wherein one or both of Z1 and Z2 are an ester group, and those wherein R is Pxe2x80x94(Spxe2x80x94X)nxe2x80x94.
Of the compounds of formula I wherein m1+m2 is 2, especially preferred are those wherein A1 and A2 are substituted or unsubstituted 1,4-phenylene in which, in addition, one or more CH groups may be replaced by N.
Of the polymerizable mesogenic compounds of formula I especially preferred are those wherein xe2x80x94(A1xe2x80x94Z1)m1xe2x80x94 and xe2x80x94(Z2xe2x80x94A2)m2xe2x80x94 are, each independently, denoting a group with one or two six-membered rings.
The groups xe2x80x94(A1xe2x80x94Z1)m1xe2x80x94 and xe2x80x94(Z2xe2x80x94A2)m2xe2x80x94 may be identical or different. Particularly preferred are compounds wherein xe2x80x94(A1xe2x80x94Z1)m1xe2x80x94 and xe2x80x94(Z2xe2x80x94A2)m2xe2x80x94 are different.
Preferred subformulae for the groups xe2x80x94(A1xe2x80x94Z1)m1xe2x80x94 and xe2x80x94(Z2xe2x80x94A2)m2xe2x80x94 are listed below. For reasons of simplicity, Phe in these groups is 1,4-phenylene, Phe L is a 1,4-phenylene group which is substituted by 1 to 4 groups L, with L being F, Cl, CN, OH, NO2 or an optionally fluorinated or optionally chlorinated alkyl, alkoxy or alkanoyl group with 1 to 7 C atoms, and Cyc is 1,4-cyclohexylene. The following list of preferred groups xe2x80x94(A1xe2x80x94Z1)m1xe2x80x94 and xe2x80x94(Z2xe2x80x94A2)m2xe2x80x94 is comprising the subformulae II-1 to II-9 as well as their mirror images, which are linked via the radical Z to the tolane group in formula I
-Phe-Zxe2x80x94xe2x80x83xe2x80x83II-1
-Cyc-Zxe2x80x94xe2x80x83xe2x80x83II-2
-PheL-Zxe2x80x94xe2x80x83xe2x80x83II-3
-Phe-Z-Phe-Zxe2x80x94xe2x80x83xe2x80x83II-4
-Phe-Z-Cyc-Zxe2x80x94xe2x80x83xe2x80x83II-5
-Cyc-Z-Cyc-Zxe2x80x94xe2x80x83xe2x80x83II-6
-PheL-Z-Phe-Zxe2x80x94xe2x80x83xe2x80x83II-7
-PheL-Z-Cyc-Zxe2x80x94xe2x80x83xe2x80x83II-8
-PheL-Z-PheL-Zxe2x80x94xe2x80x83xe2x80x83II-9
Particularly preferred are the subformulae II-1, II-3, II-7 and II-8.
In these preferred groups Z has the meaning of Z1 as given in formula I. Preferably Z is xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94CH2CH2xe2x80x94 xe2x80x94Cxe2x89xa1Cxe2x80x94 or a single bond.
Very preferably xe2x80x94(A1xe2x80x94Z1)m1xe2x80x94 and xe2x80x94(Z2xe2x80x94A2)m2xe2x80x94 are, independently of each other, selected from the following formulae and their mirror images, which are linked via the radical Z to the tolane group in formula I 
wherein Z and L have the meaning given above and r is 0, 1, 2, 3 or 4, preferably 0, 1 or 2.
The group 
in these preferred formulae is very preferably denoting 
or 
furthermore 
with L having each independently one of the meanings given above.
Particularly preferred are the subformulae IIa, IIc and IIf, in particular the subformulae IIa, IId and IIf.
Especially preferred are compounds of formula I comprising at least one group 
wherein r is 1.
Further preferred are compounds of formula I comprising at least two groups 
wherein r is 1 and/or at least one group 
wherein r is 2.
L is preferably F, Cl, CN, OH, NO2, CH3, C2H5, OCH3, OC2H5, COCH3, COC2H5, CF3, OCF3, OCHF2, OC2F5, in particular F, Cl, CN, CH3, C2H5, OCH3, COCH3 and OCF3, most preferably F, Cl, CH3, OCH3 and COCH3.
L1 and L2 in formula I preferably denote, independently of each other, F, Cl, CN, OH, NO2, CH3, C2H5, OCH3, OC2H5, CF3, OCF3, OCHF2 or OC2F5, in particular F, Cl, OCH3 or OCF3, most preferably F, Cl or OCH3. r is preferably 0, 1 or 2, most preferably 0 or 1.
If R in formula I is an alkyl or alkoxy radical, i.e. where the terminal CH2 group is replaced by xe2x80x94Oxe2x80x94, this may be straight-chain or branched. It is preferably straight-chain, has 2, 3, 4, 5, 6, 7 or 8 carbon atoms and accordingly is preferably ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, ethoxy, propoxy, butoxy, pentoxy, hexoxy, heptoxy, or octoxy, furthermore methyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, methoxy, nonoxy, decoxy, undecoxy, dodecoxy, tridecoxy or tetradecoxy, for example.
Oxaalkyl, i.e. where one CH2 group is replaced by xe2x80x94Oxe2x80x94, is preferably straight-chain 2-oxapropyl(=methoxymethyl), 2-(=ethoxymethyl) or 3-oxabutyl(=2-methoxyethyl), 2-, 3-, or 4-oxapentyl, 2-, 3-, 4-, or 5-oxahexyl, 2-, 3-, 4-, 5-, or 6-oxaheptyl, 2-, 3-, 4-, 5-, 6- or 7-oxaoctyl, 2-, 3-, 4-, 5-, 6-, 7- or 8-oxanonyl or 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-oxadecyl, for example.
In the compounds of formula I R may be an achiral or a chiral group. In case of a chiral group it is preferably selected according to the following formula III: 
wherein
X1 is xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94OCOOxe2x80x94 or a single bond,
Q1 is an alkylene or alkylene-oxy group with 1 to 10 C atoms or a single bond,
Q2 is an alkyl or alkoxy group with 1 to 10 C atoms which may be unsubstituted, mono- or polysubstituted by halogen or CN, it being also possible for one or more non-adjacent CH2 groups to be replaced, in each case independently from one another, by xe2x80x94Cxe2x89xa1Cxe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94NHxe2x80x94, xe2x80x94N(CH3)xe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94OCOxe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94COxe2x80x94 or xe2x80x94COxe2x80x94Sxe2x80x94 in such a manner that oxygen atoms are not linked directly to one another,
Q3 is halogen, a cyano group or an alkyl or alkoxy group with 1 to 4 C atoms different from Q2.
In case Q1 in formula III is an alkylene-oxy group, the O atom is preferably adjacent to the chiral C atom.
Preferred chiral groups R are 2-butyl(=1-methylpropyl), 2-methylbutyl, 2-methylpentyl, 3-methylpentyl, 2-ethylhexyl, 2-propylpentyl, 2-octyl, in particular 2-methylbutyl, 2-methylbutoxy, 2-methylpentoxy, 3-methylpentoxy, 2-ethylhexoxy, 1-methylhexoxy, 2-octyloxy, 2-oxa-3-methylbutyl, 3-oxa-4-methylpentyl, 4-methylhexyl, 2-nonyl, 2-decyl, 2-dodecyl, 6-methoxyoctoxy, 6-methyloctoxy, 6-methyloctanoyloxy, 5-methylheptyloxycarbonyl, 2-methylbutyryloxy, 3-methylvaleroyloxy, 4-methylhexanoyloxy, 2-chlorpropionyloxy, 2-chloro-3-methylbutyryloxy, 2-chloro-4-methylvaleryloxy, 2-chloro-3-methylvaleryloxy, 2-methyl-3-oxapentyl, 2-methyl-3-oxahexyl, 1-methoxypropyl-2-oxy, 1-ethoxypropyl-2-oxy, 1-propoxypropyl-2-oxy, 1-butoxypropyl-2-oxy, 2-fluorooctyloxy, 2-fluorodecyloxy for example.
In addition, compounds of formula I containing an achiral branched group R may occasionally be of importance, for example, due to a reduction in the tendency towards crystallization. Branched groups of this type generally do not contain more than one chain branch. Preferred achiral branched groups are isopropyl, isobutyl(=methylpropyl), isopentyl(=3-methylbutyl), isopropoxy, 2-methylpropoxy and 3-methylbutoxy.
Very preferably R in formula I is halogen, cyano or an optionally fluorinated achiral or chiral alkyl or alkoxy group with 1 to 15 C atoms.
Another preferred embodiment of the present invention relates to compounds of formula I wherein R is Pxe2x80x94(Spxe2x80x94X)nxe2x80x94.
P in formula I is preferably an acrylate group, a methacrylate group, a vinyl or vinyloxy group, an epoxy group, a styrene group or a propenyl ether group, in particular an acrylate, methacrylate, vinyl or epoxy group.
As for the spacer group Sp in formula I all groups can be used that are known for this purpose to the skilled in the art. The spacer group Sp is preferably a linear or branched alkylene group having 1 to 25 C atoms, especially 1 to 20 C atoms, in particular 1 to 12 C atoms, in which, in addition, one or more non-adjacent CH2 groups may be replaced by xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94NHxe2x80x94, xe2x80x94N(CH3)xe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94Oxe2x80x94COxe2x80x94, xe2x80x94Sxe2x80x94COxe2x80x94, xe2x80x94Oxe2x80x94COOxe2x80x94, xe2x80x94COxe2x80x94Sxe2x80x94, xe2x80x94COxe2x80x94Oxe2x80x94, xe2x80x94CH(halogen)xe2x80x94, xe2x80x94CH(CN)xe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94 or xe2x80x94Cxe2x89xa1Cxe2x80x94.
Typical spacer groups are for example xe2x80x94(CH2)oxe2x80x94, xe2x80x94(CH2CH2O)pxe2x80x94CH2CH2xe2x80x94, xe2x80x94CH2CH2xe2x80x94Sxe2x80x94CH2CH2xe2x80x94 or xe2x80x94CH2CH2xe2x80x94NHxe2x80x94CH2CH2xe2x80x94, with o being an integer from 2 to 12 and p being an integer from 1 to 3.
Preferred spacer groups are ethylene, propylene, butylene, pentylene, hexylene, heptylene, octylene, nonylene, decylene, undecylene, dodecylene, octadecylene, ethyleneoxyethylene, methyleneoxybutylene, ethylene-thioethylene, ethylene-N-methyliminoethylene, 1-methylalkylene, ethenylene, propenylene and butenylene for example.
Especially preferred are inventive compounds of formula I wherein Sp is an alkylene or alkylene-oxy group with 2 to 8 C atoms. Straight-chain groups are especially preferred.
In another preferred embodiment of the invention the chiral compounds of formula I comprise at least one spacer group Sp that is a chiral group of the formula IV: 
wherein
Q1 and Q3 have the meanings given in formula III, and
Q4 is an alkylene or alkylene-oxy group with 1 to 10 C atoms or a single bond, being different from Q1.
In the event that R is Pxe2x80x94Spxe2x80x94Xxe2x80x94, the two spacer groups Sp in the compounds of formula I may be identical or different.
Of the preferred compounds described above particularly preferred are those wherein n is 1.
Further preferred are compounds comprising both a group Pxe2x80x94(Spxe2x80x94X)nxe2x80x94 wherein n is 0 and a group Pxe2x80x94(Spxe2x80x94X)nxe2x80x94 wherein n is 1.
X is preferably xe2x80x94Oxe2x80x94 or a single bond.
The inventive compounds of formula I can be synthesized according to or in analogy to methods which are known per se and which are described in standard works of organic chemistry such as, for example, Houben-Weyl, Methoden der organischen Chemie, Thieme-Verlag, Stuttgart. Some specific methods of preparation can be taken from the examples.
The invention also relates to a polymerizable liquid crystal composition comprising at least two polymerizable components, at least one of which is a compound of formula I, and to linear or crosslinked polymers prepared from the inventive compounds and compositions.
Suitable polymerizable mesogenic compounds that can be used as co-components of the polymerizable liquid crystal composition, together with the inventive compounds of formula I, are disclosed for example in WO 93/22397; EP 0,261,712; DE 195,04,224; WO 95/22586 and WO 97/00600. The compounds disclosed in these documents, however, are to be regarded merely as examples that shall not limit the scope of this invention.
Typical examples representing such polymerizable mesogenic compounds are shown in the following list of compounds, which should, however, be taken only as illustrative and is in no way intended to restrict, but instead to explain the present invention: 
In the above formulae, P has one of the meanings of formula I and its preferred meanings as mentioned above, x and y are each independently 1 to 12 , A is 1,4-phenylene or 1,4-cyclohexylene, v is 0 or 1, Z0 is xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94CH2CH2xe2x80x94 or a single bond, R0 has one of the meanings of R in formula I and its preferred meanings as mentioned above, L1 and L2 have one of the meanings given above, Ter is terpene, and Chol is cholesterol.
In a preferred embodiment of the invention the polymerizable liquid crystalline composition comprises at least one monoreactive compound of formula I and at least one di- or multireactive polymerizable compound, i.e. a mesogenic compound having two or more polymerizable groups. Especially preferred are direactive compounds, i.e. compounds having two polymerizable groups. Very preferred are direactive compounds of formula I and of formulae V1 and V2 above.
It is also possible for the inventive polymerizable liquid crystalline composition to comprise one or more non-polymerizable chiral compounds, which may be mesogenic or non-mesogenic, in addition or alternatively to chiral polymerizable compounds. For example, commercially available dopants, like e.g. R 811 or R 1011 (from Merck KGaA, Germany) can be used for this purpose.
Especially preferred are chiral dopants of the following formulae 
including the respective (R,R), (S,S), (S,R) and (R,S) enantiomers not shown, wherein E and F are each independently 1,4-phenylene or trans-1,4-cyclohexylene that may be substituted with L1 as defined in formula 1, v is 0 or 1, Z0 is xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94CH2CH2xe2x80x94 or a single bond, and R1 is alkyl, alkoxy or alkanoyl with 1 to 12 C atoms.
The compounds of formula VI and their synthesis are described in WO 98/00428. The compounds of formula VII and their synthesis are described in GB 2,328,207. The above chiral compounds of formula VI and VII exhibit a very high helical twisting power (HTP), and are therefore particularly useful for the preparation of a CLC (cholesteric liquid crystal) polymer film with a short helical pitch.
Polymerizable liquid crystalline compositions are preferred that comprise 1 to 6, preferably 1 to 3 compounds of formula I.
In a preferred embodiment of the present invention the polymerizable liquid crystalline composition comprises 1 to 80% by weight, preferably 2 to 60%, in particular 5 to 50% by weight of one or more compounds of formula I.
Liquid crystalline polymers can be obtained from the inventive polymerizable compounds and compositions e.g. by solution polymerization or by in-situ polymerization.
For example, solution polymerization can be carried out in a solvent like dichloromethane, tetrahydrofuran or toluene using AIBN as an initiator and heating for 24 hours at 30 to 60xc2x0 C.
The in-situ polymerization of polymerizable liquid crystalline compounds and compositions is described in detail by D. J. Broer et al., Makromol.Chem. 190, 2255ff. and 3202ff. (1989).
The polymerizable liquid crystal compounds and compositions according to this invention are preferably polymerized in situ as described in the foregoing and the following.
The inventive compounds and polymerizable liquid crystalline compositions are particularly useful for the preparation of anisotropic polymer films, such as nematic or cholesteric polymer films, with uniform molecular orientation.
Thus, another object of the invention is an anisotropic polymer film with an oriented liquid crystalline phase that is obtainable by polymerizing a polymerizable liquid crystalline composition comprising at least one compound of formula I.
To prepare an anisotropic polymer film with uniform orientation, an inventive polymerizable mesogenic composition is preferably coated onto a substrate, aligned and polymerized in situ by exposing them to heat or actinic radiation. Alignment and curing are preferably carried out in the liquid crystalline phase of the composition.
Actinic radiation means irradiation with light, like UV light, IR light or visible light, irradiation with X-rays or gamma rays or irradiation with high energy particles, such as ions or electrons. As a source for actinic radiation for example a single UV lamp or a set of UV lamps can be used. Another possible source for actinic radiation is a laser, like e.g. a UV laser, an IR laser or a visible laser.
When polymerizing by means of UV light, for example a photoinitiator can be used that decomposes under UV irradiation to produce free radicals or ions that start the polymerization reaction. It is also possible to use a cationic photoinitiator, when curing reactive mesogens with for example vinyl and epoxide reactive groups, that photocures with cations instead of free radicals.
As a photoinitiator for radical polymerization for example the commercially available Irgacure 651, Irgacure 184, Darocure 1 173 or Darocure 4205 (all from Ciba Geigy AG) can be used, whereas in case of cationic photopolymerization the commercially available UVI 6974 (Union Carbide) can be used.
The polymerizable liquid crystalline composition preferably comprises 0.01 to 10%, in particular 0.05 to 8%, very preferably 0.1 to 5% by weight of a photoinitiator, especially preferably a UV-photoinitiator.
In addition to the components mentioned above, the polymerizable composition may also comprise one or more other suitable components such as e.g. catalysts, stabilizers, chain-transfer agents, co-reacting monomers or surface-active compounds. In particular the addition of stabilizers is preferred in order to prevent undesired spontaneous polymerization of the polymerizable material e.g. during storage.
As stabilizers in principal all compounds can be used that are known to the skilled in the art for this purpose. These compounds are commercially available in a broad variety. Typical examples for stabilizers are 4-ethoxyphenol or butylated hydroxytoluene (BHT).
Other additives, like e.g. chain transfer agents, can also be added to the polymerizable material in order to modify the physical properties of the inventive polymer film. When adding a chain transfer agent, such as monofunctional thiol compounds like e.g. dodecane thiol or multifunctional thiol compounds like e.g. trimethylpropane tri(3-mercaptopropionate), to the polymerizable material, the length of the free polymer chains and/or the length of the polymer chains between two crosslinks in the inventive polymer film can be controlled. When the amount of the chain transfer agent is increased, the polymer chain length in the obtained polymer film is decreasing.
It is also possible, in order to increase crosslinking of the polymers, to add up to 20% of a non-mesogenic compound with two or more polymerizable functional groups to the polymerizable composition alternatively or additionally to the di- or multireactive mesogenic compounds.
Typical examples for difunctional non-mesogenic monomers are alkyldiacrylates or alkyldimethacrylates with alkyl groups of 1 to 20 C atoms. Typical examples for non mesogenic monomers with more than two polymerizable groups are trimethylpropanetrimethacrylate or pentaerythritoltetraacrylate.
In a preferred embodiment of the invention the polymerization of the polymerizable composition is carried out under an atmosphere of inert gas, preferably under a nitrogen atmosphere.
As a substrate for example a glass or quarz sheet as well as a plastic film or sheet can be used. It is also possible to put a second substrate on top of the coated mixture prior to, during and/or after polymerization. The substrates can be removed after polymerization or not. When using two substrates in case of curing by actinic radiation, at least one substrate has to be transmissive for the actinic radiation used for the polymerization.
Isotropic or birefringent substrates can be used. In case the substrate is not removed from the polymerized film after polymerization, preferably isotropic substrates are used.
Preferably at least one substrate is a plastic substrate such as for example a film of polyester such as polyethyleneterephthalate (PET), of polyvinylalcohol (PVA), polycarbonate (PC) or triacetylcellulose (TAC), especially preferably a PET film or a TAC film. As a birefringent substrate for example an uniaxially stretched plastic film can be used. For example PET films are commercially available from ICI Corp. under the trade name Melinex.
In a preferred embodiment of the present invention, the inventive polymerizable composition is coated as a thin layer on a substrate or between two substrates and is aligned in its liquid crystal phase to give a uniform orientation.
A uniform orientation can be achieved for example by shearing the mixture, e.g. by means of a doctor blade. It is also possible to apply an alignment layer, for example a layer of rubbed polyimide or sputtered SiOx, on top of at least one of the substrates. In some cases, the mixtures orient themselves spontaneously on the substrate, or good alignment is achieved already by the act of coating the mixture.
In another preferred embodiment, a second substrate is put on top of the coated material. In this case, the shearing caused by putting together the two substrates is sufficient to give good alignment.
It is also possible to apply an electric or magnetic field to align the coated mixture.
In some cases it is of advantage to apply a second substrate not only to aid alignment of the polymerizable mixture but also to exclude oxygen that may inhibit the polymerization. Alternatively the curing can be carried out under an atmosphere of inert gas. However, curing in air is also possible using suitable photoinitiators and high lamp power. When using a cationic photoinitiator oxygen exclusion most often is not needed, but water should be excluded.
For the preparation of anisotropic polymer gels, e.g. for use in switchable liquid crystal display devices, the polymerizable compounds or compositions can be polymerized in situ as described above, however, in this case alignment of the polymerizable mixture is not necessarily required, although it may be desired for specific applications.
The invention also relates to the use of inventive compounds, compositions and polymers such as polarizers, optical retardation or compensation films, alignment layers, colour filters or holographic elements, in liquid crystal displays such as PDLC, polymer gel or polymer stabilized cholesteric texture (PSCT) displays, in adhesives, synthetic resins with anisotropic mechanical properties, cosmetics, diagnostics or liquid crystal pigments, for decorative and security applications, and for nonlinear optics or optical information storage. Inventive compounds comprising a chiral group can also be used as chiral dopants.
The inventive compounds of formula I are particularly suitable for the preparation of oriented liquid crystal polymer films that can be used as polarization or compensation films in liquid crystal displays.
Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The following examples are, therefore, to be construed as merely illustrative and not limitative of the remainder of the disclosure in any way whatsoever.
The entire disclosures of all applications, patents and publications, cited above and of corresponding European patent application No. 99112455.3, filed Jun. 30, 1999, are hereby incorporated by reference.